Psoriasis is a chronic inflammatory disease that affects more than the skin. Scientists now recognize it as an immunometabolic disease, meaning that changes in both the immune system and the body's metabolism contribute to its development. One area of growing interest is how the body processes tryptophan, an essential amino acid obtained from the diet.

During inflammation, tryptophan is converted into a molecule called kynurenine, which normally helps regulate the immune system by activating AhR and promoting the development of regulatory T cells that suppress excessive inflammation. In psoriasis, an enzyme called kynureninase (KYNU) is overproduced, rapidly breaking down kynurenine before it can carry out these protective effects. As a result, the immune system shifts toward inflammatory Th17 cells, increasing production of the cytokines IL-17 and IL-22 that drive abnormal skin cell growth and chronic inflammation. This process may also contribute to oxidative stress, mitochondrial dysfunction, and possibly the higher rates of depression and anxiety observed in people with psoriasis.

The kynurenine–AhR pathway is a promising area for future psoriasis research and may offer novel therapeutic opportunities. Although further studies are needed, adequate intake of tryptophan, vitamin B6, niacin, vitamin D, and zinc may complement established therapies by supporting immune and metabolic function. More broadly, this pathway likely represents one component of a larger immunometabolic network involving amino acid metabolism, JAK-STAT signaling, mitochondrial function, and micronutrient biology.